Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 edition. Excerpt: ... 217 of an air thermometer A (Fig. 217). Place a red-hot iron ball in a support B. Set up a screen S, to cut off all direct radiation toward A. Place a mirror at M, and a position can easily be found where the heat will be reflected upon A. This will heat the air and drive out part of the water from the stem. The bulb of the air thermometer should be blackened to secure the best results. 261. The Radiometer is an instrument used to detect radiant heat. It consists of a glass bulb inclosing two arms of aluminum crossing each other at right angles and carrying at each end an aluminum disk. One side of each disk is coated with lampblack while the other is bright. These arms are fastened horizontally to a vertical shaft which can rotate with them, being supported by a projection at the bottom of the bulb. When these disks are subjected to the action of radiant heat they set up a rotation, the velocity of which is dependent upon the intensity of the heat received. This apparatus can be used to show the reflection of heat as follows: Experiment 124.--Procure two concave mirrors M and M'. In the focus of M place the radiometer and in the focus of M' place an Fig. 21'J iron ball heated nearly to redness. Do not place the ball so near to the radiometer that there will be any rotation due to direct radiation. When the ball and radiometer are in the foci of their respective mirrors, the radiometer will set up a brisk rotation due to reflected radiation. Experiment 125.--Make a lighttight box, large enough to hold a radiometer. Heat a flat piece of cask iron or brass nearly to a red heat and fasten it to the inner face of the door of the box. Put the radiometer into the box and close the door. Leave it closed for about a minute and on opening it the...show more